- 著者
- Nobuo Nakada Norihide Fukuzawa Toshihiro Tsuchiyama Setsuo Takaki Tamotsu Koyano Takashi Iwamoto Yasuhiro Omori
- 出版者
- The Iron and Steel Institute of Japan
- 雑誌
- ISIJ International (ISSN:09151559)
- 巻号頁・発行日
- vol.53, no.1, pp.139-144, 2013 (Released:2013-01-15)
- 参考文献数
- 22
- 被引用文献数
- 10 13
In order to understand the mechanism of isothermal transformation of Fe–N alloy, the isothermal transformation microstructure that forms in a wide temperature range below Ae1 was investigated in Fe–2.6 mass%N hypereutectoid alloy by means of the electron back scatter diffraction method in addition to the conventional microstructural observation methods. High-nitrogen austenite fully decomposed to ferrite and Fe4N over the entire temperature range, and the time-temperature-transformation (TTT) diagram had a C shape with a nose temperature around 700 K. The hardness linearly increased with decreasing transformation temperature because the microstructure became finer, but the morphology of the (ferrite + Fe4N) structure changed discontinuously at around 800 K. From the microstructural and crystallographic analyses, it was concluded that the microstructure formed at higher temperature is a lamellar eutectoid structure, braunite, while the other is an upper bainitic structure containing bainitic ferrite formed through a displacive mechanism and Fe4N formed by concentration and ordering of the nitrogen. Since Fe4N is a counterpart of the cementite in Fe–C alloy, the respective structures are similar to pearlite and upper bainite in carbon steel.